Thrust vector steering techniques and apparatus

ABSTRACT

Single wall monostable fluidic switches and thrust vector control systems for vehicles employing such switches are disclosed. The monostable switches of the invention are characterized by small size, use of a supersonic power stream, a first operating region defining wall which terminates at a point where the power stream is over-expanded and a second operating region defining wall which falls away from the power stream axis.

United States Patent 1191 Fitzgerald [45] A 23, 1974 [5 THRUST VECTOR STEERING 3,204,405 9/1965 Warren et al 13-7/8l.5 x TECHNIQUES AND APPARATUS 2,916,873 12/1959 Walker 137/815 X 3,508,579 4/1970 Jones 137/815 X Inventor: R t t ge a e e fi 3,452,769 7/1969 Jones et al.... l37/81.5 Conn. 3,143,856 8/1964 Hausman l37/8l.5 X [73] Assignee: Chandler Evans Inc., West Hartford Com Primary Examiner-Samuel Scott Assistant Examiner-Ira S. Lazarus [22] Filed: Oct. 8, 1971 [21] App]. No.: 187,630 [57] ABSTRACT Single wall monostable fluidic switches and thrust vec- 52 U.S. c1 244/322, 239/265.l9, 137/805 Control systems for vehicles employing Such 51 1111. c1. F02k 11/00, F150 l/08 Switches are disclosed- The monostable Switches Ofthe 53 Fi of Search 137 15; 239 1 2 5 9 invention are characterized by small size, use of a su- 239/26523, 5 7 personic power stream, a first operating region defining wall which terminates at a point where the power 5 R f r Cited stream is over-expanded and a second operating re- UNITED STATES PATENTS gion defining wall which falls away from the power stream was. 3,460,554 8/1969 Johnson 137/8l.5 X 3,606,165 Ill 1969 Dunaway 239/265.27 X 20 Claims, 6 Drawing Figures PATENTEBAPR 23 I974 SHiU 1 BF 3 D L A R E m mm m E R E B O R BY f7 ATTORN EY ATENTEDAPR 2 19 3.806; 063

SHEET 3 OF 3 FIG. 6

70 LEAD-LAG REFERENCE COMPENS'ATION-+ PW PF CONTROL VEH|CLE b OUTPUT *r ATTITUDE NETWORKS MODULATOR VALVES DYNAMICS ATTITUDE (OXRDYRQZTQ i (OXQYQZ) l 72 1 ATTITUDE SENSORS TIIRUST VECTOR STEERING TECHNIQUES AND APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the control of jets of fluid. More specifically, this invention is directed to single wall monostable fluidic switches and control systems utilizing such switches. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.

2. Description of the Prior Art While not limited thereto in its utility, the present invention has been found to be particularly well suited for use in thrust vector steering systems. As is well known, partial or total control over the direction of travel of a vehicle employing a gas generator as a propulsive source can be achieved by deflecting or vectoring all or a portion of the propulsive gases at an angle to their normal flow axis.

Prior art thrust vector control systems may be classified as either mechanical or hydromechanical devices. Regardless of type, all prior art thrust vector control schemes have been characterized by comparatively large size and weight, inefficient utilization of control and propulsive fluids and less than the requisite reliability.

In order to obviate been problems inherently associated with prior art thrust vector control systems, and to improve upon previous hydromechanical-devices, it has bee proposed to borrow from the fluidics art. That is, thrust vector controls employing fluid amplifier or switch type devices have been suggested. Such fluidic devices, which rely for operation upon well known phenomena such as the Coanda effect, while theoretically offering substantial improvement over previous technology, have not found wide usage for a number of reasons. These reasons, not listed in order of importance, include excessive size, excessive control gas flow, unduly limited operable supply pressure range and lack of stability when operating into loads of varying back pressure. Considering the size limitation problem, missile dynamics permit only a shallow penetration of the missile interior for the thrust vector control device and prior art fluidic switches have not met this design criteria.

In the interest of minimizing control system size and weight, it obviously is desired to employ the propulsive gases as the power stream for a steering jet in a fluidic thrust vector control. When the power stream is derived from the propulsive engine,'economy dictates the desire for appreciable retention of the axial thrust of the gases passing through the control devices when lateral thrust is not needed for steering. Prior art devices and systems have been able to meet this desirable design criteria only through the use of valves for shutting off the engine exhaust derived power stream or streams. The employment of valves for this purpose increased the size and weight of the control systems and devices while decreasing their reliability.

A further deficiency of prior art fluidic control systems has resided in the fact that the switching function was dependent upon supply pressure and thus the devices were operable only over a rather limited range of control pressures. Even within this limited pressure range it has been necessary to employ control ports and control valves of comparatively large size since the sole determining factor with respect to the achieving of switching has been the means for regulating the control gas flow or pressure. Restated, prior art fluidic switch designs have not provided for biasing the devices whereby the opening of a small control port and injection of small additional flow will immediately result in the switching. In short, prior art fluidic switches have been lacking in sensitivity and speed of operation.

It is also to be noted that prior art thrust vector controls have been susceptible to thermal damage and/or lack of consistent operation due to size and shape variations caused by expansion induced by the close proximity to the hot exhaust gases from the main propulsive source. It would, of course, be desirable to insulate the walls of the control devices from the hot gases which are both directed therethroughand flowing adjacent thereto. The provision of such insulation has, however, previously been thought to be inconsistent with size requirements as discussed above.

SUMMARY OF THE INVENTION The present invention overcomes discussed and other disadvantages and deficiencies of the prior art by providing novel monostable fluidic switches particularly well suited for use in thrust vector control systems and vehicle steering systems employing such switches. The switches in accordance with the present invention operate with a power stream which attains supersonic velocity in the operating or reaction region and the switches are characterized by a single wall construction wherein the first or outboard wall defining the reaction region is terminated at a point where it is contacted by the over expanded power jet. The second or opposite reaction region defining wall is designed in such a manner as to prevent the impingement of strong shocks thereon and flares away from the axis of the power jet whereby the pressure within the jet is maintained at a subambient level and the pressure differential across the jet boundary causes the power stream to follow the second wall in its normal or stable state. The invention is further characterized by one or more control ports in the second or inboard wall, the control ports and their associated control valves being employed to deliver fluid at ambient pressure to the operating region thereby equalizing the pressure differential across the power jet when it is desired to switch the jet off the second wall. The monostable fluidic switches in accordance with the present invention may also be provided with a biasing port or ports which enhance the sensitivity and operational speed of the devices and provide a small insulating flow of ambient gas.

The invention also encompasses control systems employing the above briefly described single wall monostable fluidic switches. These control systems employ a plurality of switches which may be operated either singly or in pairs with the control valves for the switches being provided with pulse modulated error signals. The switches in a thrust vector steering system may be located off-axis if roll control is desired.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the acthe above- 7 companying drawing wherein like reference numerals refer to like elements in the several figures and in which:

FIG. 1 depicts, partly in section, a missile employing a thrust vector control system in accordance with the present invention;

FIG. 2 is a cross-sectional, end view of the control system of FIG. 1;

FIG. 3 is a cross-sectional, side view of the first embodiment of a single wall, monostable fluidic switch in accordance with the present invention, the switch of FIG. 3 being applicable to the system of FIGS. 1 and 2;

FIG. 4 is a side view ofa second embodiment ofa single wall, monostable fluidic switch in accordance with the present invention;

FIG. 5 is a bottom view of the switch of FIG. 4; and

FIG. 6 is a block diagram of control circuitry which may be employed in the steering system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. l, a missile indicated generally at It) employs a plurality of single wall monostable fluidic switches in a thrust vector control in accordance with the present invention. In the basic configuration of FIG. 1, which shows missile l0 partially in cross-section, four separate fluidic switches are employed. As may be seen from joint consideration of FIGS. 1 and 2, the switches 12, 14, 16 and 18 are each located slightly off-axis thereby enabling the control system to be employed for both steering and roll control. Roll control may be achieved through operating, into the lateral thrust state, the switches of an opposed pair. The first pair of switches will in roll n a first direction through generation of a force component or roll couple and the other pair of switches, located 90 from the switches of the first pair, will cause roll in the opposite direction. It will be understood that when only one device is switched to the lateral thrust state for steering a slight unwanted roll moment will occur and pulsing of an opposed roll pair may be required in order to provide compensation for this unwanted roll moment. If roll control is deemed unnecessary or undesirable, the fluidic switches 112, 14, 16 and E8 may be arranged in diametrically opposed pairs rather than off-axis as shown.

F108. 1 and 3 clearly show one of the principal attributes of the present invention. As noted above, prior art fluidic thrust vector control concepts had the distinct disadvantage of employing individual switches having a configuration which required, for installation, a substantial penetration of the side walls of the missile. As depicted in FIGS. 11 and 3, the present invention requires only a very shallow penetration of the missile interior; this shallow penetration being in part attributable to the fact that the monostable fluidic switches in accordance with the invention are substantially single wall devices. Thus, as may most clearly be seen from FIG. 3., a first or outboard wall 20 of switch 12 terminates a short distance downstream of the port 22 through which the power stream flows while the second or inboard wall 24 is contoured so as to merge with the missile skin surface. Thus, as will be explained in more detail below, wall 24 is not straight but rather is curved or segmented in the interest of achieving maximum lateral force while also achieving maximum turning of the lateral jet into the axial direction and, of course, for best fit to the missile surface. The turning of the jet emanating from the fluidic switch in the axial direction results in appreciable retention of axial thrust when lateral thrust is not needed for steering.

Before further discussing the embodiment of FIG. 3, it is believed desirable to describe the embodiment of a monostable single wall fluidic switch shown in FIGS. 4 and 5. The switch of FIGS. 4 and 5 includes an entrance connector 30 which is adapted to be coupled to the power stream source. In the case of a missile thrust vector control, connector 30 may be exposed to the exhaust gas stream produced by the missile gas generator or engine. Connector 30 discharges, via a slot-shaped port 32, into the operating or reaction region 34 of the switch. Port 32, in cooperation with the connector 30 and the oppositely disposed walls 36 and 38 of the operating region 34, defines a convergent-divergent nozzle. The configuration of this nozzle, in combination with the power stream source pressure, results in the power stream discharged into operating region 34 attaining supersonic velocity.

It is to be noted that walls 36 and 38 which define the upstream end of operating region 34 are respectively provided with offsets 40 and 42 adjacent the exit end of port 32. Since the fluid injected into operating region 34 attains supersonic velocity, the power jet will expand and will contact both of walls 36 and 38 a short distance downstream of port 32. As is well known, the pressure in such an over expanded stream is subambient. It is also known that there is a transition from ambient to subambient pressure across a shock wave. Accordingly, the power stream pressure may be kept subambient by preventing strong shocks resulting from impingement of the stream on the walls of the reaction chamber.

As noted, the fluidic switches of the present invention are monostable devices. The stable mode of operation is with the power stream following the contour of reaction chamber wall 36. The direction of the power stream toward wall 36 under the stable operating condition is achieved through making the set-back 42 of wall 38 larger than setback 40 of wall 36 whereby there is more room for expansion of the power stream toward wall 38. Also, wall 33 is terminated at a point where it is contacted by the over expanded power stream. Accordingly, downstream of the termination of wall 38 there will be a pressure differential across the boundary of the power stream and the higher or ambient pressure will force the power stream toward wall 36.

The power stream will be caused to follow the contour of wall 36 by maintaining the stream pressure below ambient. This is achieved by shaping the wall in such a manner that strong shocks are prevented. The flow along wall 36 will, of course, separate and thereafter reattach to the wall at one or more locations depending upon the wall length and recirculation regions wherein the pressure is less than ambient will be established between the points of separation and reattachment. The AP across the stream resulting from creation of these low pressure recirculation regions will aid in holding the power stream along wall 36.

The embodiment of FIGS. 4 and 5 is provided with a control port 44 whereby switching from the stable to unstable modes may be achieved. Considering application of the monostable switch of the present invention in a thrust vector control, lateral steering thrust may be generated by opening control port 44, which may be in the form of a slot as shown, to ambient pressure. When control port 44 is opened to ambient pressure, through the use of valve means not shown in FIGS. 4 and 5, the pressure differential across the stream will be equalized and the power stream will switch off of wall 36 and tend to flow in a path commensurate with the axis of inlet connector 30. Isolation of port 44 from ambient pressure will cause the stream to again follow wall 36 since the pressure differential across the power stream will almost instantaneously be reestablished when no flow into the reaction chamber 34 through port 44 is permitted. In the embodiment of FIGS. 4 and 5, the source of ambient pressure for control port 44, including the control valve, will be connected to the monostable switch via a connector 46.

FIG. 4 also depicts a plurality of bias ports 48, 48', 48". These bias ports are normally open and provide for the injection of a very limited amount of fluid at ambient pressure into the reaction chamber along wall 36. Through the use of biasing ports 48, the pressure differential across the power stream will be maintained slightly above the switching level. Accordingly, the establishment of communication between port 44 and the ambient atmosphere will result in rapid switching of the stream off wall 36 thereby achieving sensitive and rapid response of the switch. Depending on the particular application, the bias ports 48 may be omitted. When the bias ports are included, the flow therethrough provides a measure of thermal insulation for the switch.

Returning to a consideration of the embodiment of FIG. 3, it may be seen that the inboard wall 24 is defined by a plurality of straight segments as opposed to being a curved surface as in the case of wall 36 of the embodiment of FIG. 4. Whether the wall is straight or curved, the same primary design consideration applies. That is, the inboard wall of the monostable switch falls away from the axis of the stream entering the reaction chamber and in so doing defines a shape which will tend to maintain subambient pressure. In order to achieve the foregoing objective, the inboard wall 24 of the embodiment of FIG. 3 is designed to prevent strong shocks from impinging thereon. Wall 24 thus generally conforms to the shock wave which will emanate from the point of termination of outboard wall 20. This shock wave is indicated at A in FIG. 3.

In the embodiment of FIG. 3, each of the segments 24, 24" and 24 of inboard wall 24 is provided with a separate control port. Each control port has, associated therewith, a separate valve whereby the ports may be opened independently to ambient pressure. In FIG. 3 the valves are shown schematically at 60, 62 and 64. Depending on the amount of lateral steering thrust needed, the control valves are individually opened with opening of valve 60 providing maximum obtainable lateral thrust and opening of valve 64 providing minimum obtainable lateral steering thrust.

The embodiment of FIG. 3 is also provided with a source of bias fluid 66 and its associated port 68. In the FIG. 3 embodiment the biasing port is located upstream of the first or primary control port in wall segment 24' whereas in the embodiment of FIG. 4 a plurality of biasing ports positioned downstream of the control port are employed. In either case the bias ports serve the same functions and in the same manner.

In the cross sectional view of FIG. 1, in the interest of facilitating understanding of the drawing, only the primary control ports have been shown. In FIG. 1 switch 14 is depicted operating in the stable mode and the power stream follows the contour of the inboard wall whereby it adds to the axial thrust of the gases passing out through the main exhaust nozzle of the engine. Switch 12 is shown as operating in the unstable or lateral steering thrust producing mode wherein the primary control port is opened to ambient pressure and the power stream has switched away from the inboard wall.

FIG. 6 is a block diagram of a control circuit for a thrust vector control system employing the monostable fluidic switches of the present invention. Pitch, yaw and roll error signals will be generated by comparison circuitry which has, applied as the input thereto, reference information commensurate with the desired attitude of the vehicle and feedback information commensurate with the actual attitude. The actual attitude information is sensed by appropriate transducers, which do not constitute part of the present invention and are indicated generally at 72, which may comprise accelerometers or other state of the art apparatus. The attitude reference information may be provided by on-board computers or ground stations and transmitted to the vehicle. Error information provided by comparison circuitry 70 is applied to a plurality of lead-lag compensation networks, indicated at 74, and in the manner well known in the art the compensation networks will provide appropriate control signals for each control valve. The signals generated by the compensation networks are applied to pulse width-pulse frequency modulators associated with each control valve. Pulse width-pulse frequency modulators suitable for use with the present invention are described in an article entitled A New Pulse Modulator for Accurate DC Amplification with Linear or Nonlinear Devices by R. A. Schaefer which appeared in the IRE Transactions on Instrumentation, September 1962, pages 34-47, which article is incorporated herein by reference. As noted, there will be a separate modulator 76 for each of the control valves; the valves for the fluidic switches being indicated in FIG. 6 at 80. The use of pulse-frequency pulse-width modulation for the control of the valves which in turn control the lateral thrust producing fluidic switches results in high accuracy and wide dynamic range. The control valves, of course, are capable of off-on operation only whereas the control system response should provide an average steering thrust proportional to the particular attitude error being corrected. By utilizing the pulse ratio modulation obtainable with pulse width-pulse frequency modulators, operation of the control valves for the steering jets is limited to within a certain minimum pulse width; the maximum repetition frequency with the minimum width being determined by the response capabilities of the fluidic switches being controlled.

While preferred embodiments of monostable fluidic switches and of a thrust vector control system applying such switches have been described, various modifications and substitutions may be made to the described apparatus without departing from the spirit and scope of the invention. Thus, for example, the control jets may be located at other points on a vehicle rather than adjacent the main engine exhaust nozzle as shown in FIG. 1. Also, .while the invention has been described in terms of employing propulsive gases generated by the vehicle engine for the lateral steering jets, other gas sources including ram air may be utilized. Thus, it may be seen that the present invention has been described by way of illustration and not limitation.

What is claimed is:

l. A steering system for a vehicle comprising: a plurality of monostable fluidic switches, said switches being recessed in the vehicle in spaced apart relationship, said switches each discharging a stream of fluid to the exterior of the vehicle, said switches each including: means for imparting supersonic velocity to a stream of fluid delivered thereto from the interior of the vehicle; a first wall positioned downstream of said supersonic velocity imparting means and offset therefrom, said first wall terminating at a point where the stream of supersonic fluid is over-expanded and contacts the wall; a second wall disposed oppositely of said first wall and cooperating therewith to in part define an operating region located downstream of said supersonic velocity imparting means, said second wall merging with the exterior surface of the vehicle downstream of a point opposite the termination of said first wall, said second wall being generally inclined away from the axis of the stream, the contour of said second wall suppressing the generation of shock waves whereby the stream will normally follow said second wall; and at least a first control point located in said second wall; means associated with each of said fluidic switches for applying control pressure to said control parts, application of said control pressure causing the streams to switch from the second walls of the switches thereby generating thrust components at an angle to the vehicle exterior surface; and

means responsive to vehicle attitude error signals for selectively energizing said control pressure applying means.

2. The apparatus of claim ll wherein said control pressure applying means each comprise:

means providing communication between the control port and a source of fluid at ambient pressure; and

solenoid operated valve means disposed in said communication providing means.

3. The apparatus of claim 2 wherein said means for selectively energizing said control pressure applying means comprises:

means responsive to attitute error signals for generating pulsating electrical control signals for application to said solenoid operated valves.

4. The apparatus of claim 1 wherein the vehicle to be steered is at least partly cylindrical in shape and wherein at least four fluidic switches are spaced equally about the periphery of the cylindrical portion.

5. The apparatus of claim 41 wherein said four fluidic switches are arranged in oppositely disposed pairs located off axis whereby said switches may be energized in pairs to provide roll control.

6. The apparatus of claim ll wherein each of said switches further includes:

bias port means located in said second wall; and

means for delivering a bias flow of fluid at ambient pressure to said bias port means.

7. The apparatus of claim 1 wherein the second wall of each of said fluidic switches comprises a plurality of straight segments.

8. The apparatus of claim 1 wherein the means for imparting supersonic velocity to the stream of fluid in each of said switches comprises:

means cooperating with the operating regions dc fined in part by said first and second walls to define a convergent-divergent nozzle; and

means for delivering pressurized fluid to the convergent portion of said nozzle.

9. The apparatus of claim 8 wherein said nozzle defining means comprises:

a wall defining a first end of said operating region, said wall being provided with a slot which defines the throat of the nozzle; and

conduit means having a cross-sectional area in excess of the cross-sectional area of said slot located upstream of said slot.

110. The apparatus of claim 9 wherein said second wall is offset from said slot, the offset of said second wall being less than the offset of said first wall.

11. The apparatus of claim 10 wherein said control pressure applying means each comprise:

means providing communication between the control port and a source of fluid at ambient pressure; and

solenoid operated valve means disposed in said communication providing means.

12. The apparatus of claim ll 1 wherein said means for selectively energizing said control pressure applying means comprises:

means responsive to attitude error signals for generating pulsating electrical control signals for application to said solenoid operated valves.

13. The apparatus of claim 12 wherein each of said switches further includes:

bias port means located in said second wall; and

means for delivering a bias flow of fluid at ambient pressure to said bias port means.

14. A monostable fluidic switch comprising:

means defining the convergent portion of a convergent-divergent nozzle, said convergent nozzle portion defining means being adapted to be connected to a source of pressurized fluid;

means defining the divergent portion of said nozzle, said divergent nozzle portion defining means being located downstream of said convergent portion defining means and in communication therewith whereby fluid delivered to said nozzle means will be discharged into said divergent portion at supersonic velocity, said divergent portion defining means including:

first and second oppositely disposed side walls;

a third side wall extending between said first and second walls, said third wall terminating at a point where the stream of supersonic fluid delivered to said divergent nozzle portion will be overexpanded and will contact said third wall; and

a fourth side wall disposed oppositely of said third wall, said fourth wall extending downstream from a point opposite the termination of said third wall and being generally inclined away from the axis of said nozzle; at least a first control port located in said fourth wall; and

fourth walls are set back from the throat of the nozzle, said third wall being displaced from the throat by a greater distance than said fourth wall.

17. The apparatus of claim 16 wherein said control pressure delivering means comprises:

conduit means establishing communication between said control port and the ambient atmosphere; and

valve means disposed within said conduit means.

18. The apparatus of claim 17 further comprising:

a bias port located in said fourth wall; and

means for delivering fluid at ambient pressure to said bias port.

19. The apparatus of claim 16 wherein said fourth wall comprises a plurality of straight segments.

20. The apparatus of claim 19 further comprising:

a control port disposed in each straight segment of said fourth wall;

conduit means for providing communication between each of said control ports and the ambient atmosphere; and

valve means interposed each of said conduit means. 

1. A steering system for a vehicle comprising: a plurality of monostable fluidic switches, said switches being recessed in the vehicle in spaced apart relationship, said switches each discharging a stream of fluid to the exterior of the vehicle, said switches each including: means for imparting supersonic velocity to a stream of fluid delivered thereto from the interior of the vehicle; a first wall positioned downstream of said supersonic velocity imparting means and offset therefrom, said first wall terminating at a point where the stream of supersonic fluid is over-expanded and contacts the wall; a second wall disposed oppositely of said first wall and cooperating therewith to in part define an operating region located downstream of said supersonic velocity imparting means, said second wall merging with the exterior surface of the vehicle downstream of a point opposite the termination of said first wall, said second wall being generally inclined away from the axis of the stream, the contour of said second wall suppressing the generation of shock waves whereby the stream will normally follow said second wall; and at least a first control point located in said second wall; means associated with each of said fluidic switches for applying control pressure to said control parts, application of said control pressure causing the streams to switch from the second walls of the switches thereby generating thrust components at an angle to the vehicle exterior surface; and means responsive to vehicle attitude error signals for selectively energizing said control pressure applying means.
 2. The apparatus of claim 1 wherein said control pressure applying means each comprise: means providing communication between the control port and a source of fluid at ambient pressure; and solenoid operated valve means disposed in said communication providing means.
 3. The apparatus of claim 2 wherein said means for selectively energizing said control presSure applying means comprises: means responsive to attitute error signals for generating pulsating electrical control signals for application to said solenoid operated valves.
 4. The apparatus of claim 1 wherein the vehicle to be steered is at least partly cylindrical in shape and wherein at least four fluidic switches are spaced equally about the periphery of the cylindrical portion.
 5. The apparatus of claim 4 wherein said four fluidic switches are arranged in oppositely disposed pairs located off axis whereby said switches may be energized in pairs to provide roll control.
 6. The apparatus of claim 1 wherein each of said switches further includes: bias port means located in said second wall; and means for delivering a bias flow of fluid at ambient pressure to said bias port means.
 7. The apparatus of claim 1 wherein the second wall of each of said fluidic switches comprises a plurality of straight segments.
 8. The apparatus of claim 1 wherein the means for imparting supersonic velocity to the stream of fluid in each of said switches comprises: means cooperating with the operating regions defined in part by said first and second walls to define a convergent-divergent nozzle; and means for delivering pressurized fluid to the convergent portion of said nozzle.
 9. The apparatus of claim 8 wherein said nozzle defining means comprises: a wall defining a first end of said operating region, said wall being provided with a slot which defines the throat of the nozzle; and conduit means having a cross-sectional area in excess of the cross-sectional area of said slot located upstream of said slot.
 10. The apparatus of claim 9 wherein said second wall is offset from said slot, the offset of said second wall being less than the offset of said first wall.
 11. The apparatus of claim 10 wherein said control pressure applying means each comprise: means providing communication between the control port and a source of fluid at ambient pressure; and solenoid operated valve means disposed in said communication providing means.
 12. The apparatus of claim 11 wherein said means for selectively energizing said control pressure applying means comprises: means responsive to attitude error signals for generating pulsating electrical control signals for application to said solenoid operated valves.
 13. The apparatus of claim 12 wherein each of said switches further includes: bias port means located in said second wall; and means for delivering a bias flow of fluid at ambient pressure to said bias port means.
 14. A monostable fluidic switch comprising: means defining the convergent portion of a convergent-divergent nozzle, said convergent nozzle portion defining means being adapted to be connected to a source of pressurized fluid; means defining the divergent portion of said nozzle, said divergent nozzle portion defining means being located downstream of said convergent portion defining means and in communication therewith whereby fluid delivered to said nozzle means will be discharged into said divergent portion at supersonic velocity, said divergent portion defining means including: first and second oppositely disposed side walls; a third side wall extending between said first and second walls, said third wall terminating at a point where the stream of supersonic fluid delivered to said divergent nozzle portion will be over-expanded and will contact said third wall; and a fourth side wall disposed oppositely of said third wall, said fourth wall extending downstream from a point opposite the termination of said third wall and being generally inclined away from the axis of said nozzle; at least a first control port located in said fourth wall; and means for delivering control pressure to said control port.
 15. The apparatus of claim 14 further comprising: a bias port located in said fourth wall; and means for delivering fluid at ambient pressure to said bais port.
 16. The apparatus of claim 14 wherein said third and fourth walls are set back from the throat of the nozzle, said third wall being displaced from the throat by a greater distance than said fourth wall.
 17. The apparatus of claim 16 wherein said control pressure delivering means comprises: conduit means establishing communication between said control port and the ambient atmosphere; and valve means disposed within said conduit means.
 18. The apparatus of claim 17 further comprising: a bias port located in said fourth wall; and means for delivering fluid at ambient pressure to said bias port.
 19. The apparatus of claim 16 wherein said fourth wall comprises a plurality of straight segments.
 20. The apparatus of claim 19 further comprising: a control port disposed in each straight segment of said fourth wall; conduit means for providing communication between each of said control ports and the ambient atmosphere; and valve means interposed each of said conduit means. 